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LTC4002 Standalone Li-Ion Switch Mode Battery Charger
FEATURES
DESCRIPTIO

Wide Input Supply Range: 4.7V to 22V - 4.2 Version 8.9V to 22V - 8.4 Version High Efficiency Current Mode PWM Controller with 500kHz Switching Frequency 1% Charge Voltage Accuracy End-of-Charge Current Detection Output 3 Hour Charge Termination Timer Constant Switching Frequency for Minimum Noise 5% Charge Current Accuracy Low 10A Reverse Battery Drain Current Automatic Battery Recharge Automatic Shutdown When Input Supply is Removed Automatic Trickle Charging of Low Voltage Batteries Battery Temperature Sensing and Charge Qualification Stable with Ceramic Output Capacitor 8-Lead SO and 10-Lead DFN Packages
The LTC(R)4002 is a complete battery charger controller for one (4.2V) or two (8.4V) cell lithium-ion batteries. With a 500kHz switching frequency, the LTC4002 provides a small, simple and efficient solution to fast charge Li-Ion batteries from a wide range of supply voltages. An external sense resistor sets the charge current with 5% accuracy. An internal resistor divider and precision reference set the final float voltage to 4.2V per cell with 1% accuracy. When the input supply is removed, the LTC4002 automatically enters a low current sleep mode, dropping the battery drain current to 10A. An internal comparator detects the near end-of-charge condition while an internal timer sets the total charge time and terminates the charge cycle. After the charge cycle ends, if the battery voltage drops below 4.05V per cell, a new charge cycle will automatically begin. The LTC4002 is available in the 8-lead SO and 10-lead DFN packages.
, LTC and LT are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.
APPLICATIO S

Portable Computers Charging Docks Handheld Instruments
TYPICAL APPLICATIO
1.5A Single Cell Li-Ion Battery Charger
VIN 5V TO 22V
100
90
0.1F BAT 2k
VCC GATE LTC4002ES8-4.2
10F
EFFICIENCY (%)
80
CHARGE STATUS CHRG SENSE
6.8H
70
68m COMP NTC BAT GND 22F 10k T NTC NTC: DALE NTHS-1206N02
60 5 10 15 INPUT VOLTAGE (V)
4002 TA02
0.47F 2.2k
+
Li-Ion BATTERY
4002 TA01
U
Efficiency vs Input Voltage
(CURVES INCLUDE INPUT DIODE) VBAT = 4V VBAT = 3.8V 20 25
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1
LTC4002
ABSOLUTE
AXI U RATI GS (Note 1)
Operating Temperature Range (Note 4) .. - 40C to 85C Storage Temperature Range ................. - 65C to 125C Lead Temperature (S8 Package) (Soldering, 10 sec) ........................................... 300C
Supply Voltage (VCC) .............................................. 24V GATE .................................................. (VCC - 8V) to VCC BAT, SENSE .............................................. - 0.3V to 14V CHRG, NTC ................................................. - 0.3V to 8V
PACKAGE/ORDER I FOR ATIO
TOP VIEW COMP VCC GATE PGND SGND 1 2 3 4 5 11 10 NC 9 NTC 8 SENSE 7 BAT 6 CHRG
ORDER PART NUMBER LTC4002EDD-4.2 LTC4002EDD-8.4 DD PART MARKING LAGG LBGY
COMP 1 VCC 2 GATE 3 GND 4
DD PACKAGE 10-LEAD (3mm x 3mm) PLASTIC DFN TJMAX = 125C, JA = 43C/W EXPOSED PAD IS GND (PIN 11) MUST BE SOLDERED TO PCB
Consult LTC Marketing for parts specified with wider operating temperature ranges.
(LTC4002-4.2) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 10V unless otherwise noted.
SYMBOL VCC ICC PARAMETER VCC Supply Voltage VCC Supply Current Current Mode Shutdown Mode Sleep Mode 5V VCC 22V (Note 2)
ELECTRICAL CHARACTERISTICS
CONDITIONS
DC Characteristics 4.7 3 3 10 4.168 4.158 93 90 5 2.75 3.9 200 4.2 100 10 2.9 4.2 200 COMP Pin Falling VCC - VBAT VCOMP = 1.2V VCHRG = 1V ICHRG = 1mA VSNS(EOC)/VSNS(CHG) 10 15 360 250 100 25 0.15 25 35 0.3 32 10 500 22 5 5 20 4.232 4.242 107 110 15 3.05 4.5 V mA mA A V V mV mV mV V V mV mV mV A A V % %
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VBAT(FLT)
Battery Regulated Float Voltage
VSNS(CHG) Constant Current Sense Voltage VSNS(TRKL) Trickle Current Sense Voltage VTRKL VUV VUV VMSD VASD ICOMP ICHRG VCHRG REOC tTIMER Trickle Charge Threshold Voltage VCC Undervoltage Lockout Threshold Voltage VCC Undervoltage Lockout Hysteresis Voltage Manual Shutdown Threshold Voltage Automatic Shutdown Threshold Voltage COMP Pin Output Current CHRG Pin Weak Pull-Down Current CHRG Pin Output Low Voltage End-of-Charge Ratio Charge Time Accuracy
3V VBAT 4V (Note 3) VBAT = 0V (Note 3) VBAT Rising VCC Rising
2
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TOP VIEW 8 7 6 5 NTC SENSE BAT CHRG
ORDER PART NUMBER LTC4002ES8-4.2 LTC4002ES8-8.4 S8 PART MARKING 400242 400284
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 110C/W
MIN
TYP
MAX
UNITS
0C TA 85C -40C TA 85C

LTC4002
(LTC4002-4.2) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 10V unless otherwise noted.
SYMBOL INTC VNTC-HOT PARAMETER NTC Pin Output Current NTC Pin Threshold Voltage (Hot) CONDITIONS VNTC = 0.85V VNTC Falling Hysteresis VNTC Rising Hysteresis VBAT(FULLCHARGED) - VRECHRG, VBAT Falling VCHRG = 8V, Charging Stops 450 500

ELECTRICAL CHARACTERISTICS
MIN 75 340 2.428 100
TYP 85 355 25 2.465 170 150
MAX 95 370 2.502 200 1 550 100
UNITS A mV mV V mV mV A kHz % ns ns
VNTC-COLD NTC Pin Threshold Voltage (Cold) VRECHRG Recharge Battery Voltage Offset from Full Charged Battery Voltage ILEAK Oscillator fOSC DC Gate Drive tr tf VGATE VGATEHI VGATELO Rise Time Fall Time Output Clamp Voltage Output High Voltage Output Low Voltage Switching Frequency Maximum Duty Cycle CHRG Pin Leakage Current
CGATE = 2000pF, 10% to 90% CGATE = 2000pF, 90% to 10% VCC - VGATE, VCC 9V VGATEHI = VCC - VGATE, VCC 7V VGATELO = VCC - VGATE, VCC 7V

20 50 8 0.3 4.5
V V V
(LTC4002-8.4) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 12V unless otherwise noted.
SYMBOL VCC ICC PARAMETER VCC Supply Voltage VCC Supply Current Current Mode Shutdown Mode Sleep Mode 9V VCC 22V (Note 2)
CONDITIONS
MIN 8.9
TYP
MAX 22
UNITS V mA mA A V V mV mV mV V V mV mV mV A
DC Characteristics 3 3 10 8.336 8.316 95 93 5 4.7 8.4 100 100 10 5 7.5 500 COMP Pin Falling VCC - VBAT VCOMP = 1.2V VCHRG = 1V ICHRG = 1mA VSNS(EOC)/VSNS(CHG) VNTC = 0.85V
5 5 20 8.464 8.484 105 107 15 5.3 8.5 500
VBAT(FLT)
Battery Regulated Float Voltage
VSNS(CHG) Constant Current Sense Voltage 6V VBAT 8V (Note 3) VSNS(TRKL) Trickle Current Sense Voltage VTRKL VUV VUV VMSD VASD ICOMP ICHRG VCHRG REOC tTIMER INTC Trickle Charge Threshold Voltage VCC Undervoltage Lockout Threshold Voltage VCC Undervoltage Lockout Hysteresis Voltage Manual Shutdown Threshold Voltage Automatic Shutdown Threshold Voltage COMP Pin Output Current CHRG Pin Weak Pull-Down Current CHRG Pin Output Low Voltage End-of-Charge Ratio Charge Time Accuracy NTC Pin Output Current VBAT = 0V (Note 3) VBAT Rising VCC Rising
200
350 250 100
15 5 75
25 0.15 10 85
35 0.3 15 10 95
A V % % A
4002f
3
LTC4002
(LTC4002-8.4) The denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VCC = 12V unless otherwise noted.
SYMBOL VNTC-HOT PARAMETER NTC Pin Threshold Voltage (Hot) CONDITIONS VNTC Falling Hysteresis VNTC Rising Hysteresis VBAT(FULLCHARGED) - VRECHRG, VBAT Falling VCHRG = 8V, Charging Stops 450 500

ELECTRICAL CHARACTERISTICS
MIN 340 2.428 200
TYP 355 25 2.465 170 300
MAX 370 2.502 400 1 550 100
UNITS mV mV V mV mV A kHz % ns ns
VNTC-COLD NTC Pin Threshold Voltage (Cold) VRECHRG Recharge Battery Voltage Offset from Full Charged Battery Voltage ILEAK Oscillator fOSC DC Gate Drive tr tf VGATE VGATEHI VGATELO Rise Time Fall Time Output Clamp Voltage Output High Voltage Output Low Voltage Switching Frequency Maximum Duty Cycle CHRG Pin Leakage Current
CGATE = 2000pF, 10% to 90% CGATE = 2000pF, 90% to 10% VCC - VGATE VGATEHI = VCC - VGATE VGATELO = VCC - VGATE

20 50 8 0.3 4.5
V V V
Note 1: Absolute Maximum Rating are those values beyond which the life of a device may be impaired. Note 2: The LTC4002 is tested with Test Circuit 1. Note 3: The LTC4002 is tested with Test Circuit 2.
Note 4: The LTC4002 is guaranteed to meet performance specifications from 0C to 70C. Specifications over the - 40C to 85C operating temperature range are assured by design, characterization and correlation with statistical process controls.
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Temperature
4.0
4
3.5
3
fOSC (kHz)
ICC (mA)
ICC (mA)
3.0
2.5 -50 -25
50 25 75 0 TEMPERATURE (C)
4
UW
100
4002 G01
TA = 25C, VCC = 10V unless otherwise noted. Oscillator Frequency vs Temperature
550
Supply Current vs VCC
CURRENT MODE
500
125
2
5
10
15 VCC (V)
20
25
4002 G02
450 - 50 - 25
0
50 75 25 TEMPERATURE (C)
100
125
4002 G03
4002f
LTC4002 TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency vs VCC
510 8
500
VCHRG (mV)
fOSC (kHz)
VUV (V)
490
5
10
15 VCC (V)
20
CHRG Pin Output Low Voltage vs Temperature
180 ILOAD = 1mA 29
ICHRG (A)
VCHG (mV)
ICHRG (A)
140
100 - 50 - 25
0
50 75 25 TEMPERATURE (C)
Recharge Voltage Offset Per Cell from Full Charged Voltage vs Temperature
190
160
VRECHRG/CELL (mV)
VRECHRG (mV)
VRECHRG (mV)
150
110 - 50 - 25
0
50 75 25 TEMPERATURE (C)
UW
4002 G04
TA = 25C, VCC = 10V unless otherwise noted. CHRG Pin Output Low Voltage vs VCC
150 ILOAD = 1mA
Undervoltage Lockout Threshold vs Temperature
VCC RISING LTC4002-8.4 7
6
140
5 LTC4002-4.2 25 4 - 50 - 25 130 0 50 75 25 TEMPERATURE (C) 100 125 5 15 VCC (V)
4002 G05 4002 G06
10
20
25
CHRG Pin Weak Pull-Down Current vs Temperature
VCHRG = 8V
28
CHRG Output Pin Weak Pull-Down Current vs VCC
VCHRG = 8V
25
25
100
125
21 - 50 - 25
22
0
50 75 25 TEMPERATURE (C)
100
125
5
10
15 VCC (V)
20
25
4002 G09
4002 G07
4002 G08
Recharge Voltage Offset from Full Charged Voltage vs VCC
LTC4002-4.2
Recharge Voltage Offset from Full Charged Voltage vs VCC
320 LTC4002-8.4
150
300
100
125
140
280
5 10 15 VCC (V) 20 25
4002 G11
5
10
15 VCC (V)
20
25
4002 G12
4002 G10
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5
LTC4002 TYPICAL PERFOR A CE CHARACTERISTICS
Current Mode Sense Voltage vs Temperature
104 102
VSNS (mV)
VSNS (mV)
100
100
VSNS (mV)
96 - 50 - 25
0
50 75 25 TEMPERATURE (C)
COMP Pin Output Current vs VCC
102 VCOMP = 0V 104
ICOMP (A)
ICOMP (A)
100
INTC (A)
98
5
10
15 VCC (V)
20
Trickle Charge Voltage vs Temperature
3.0 LTC4002-4.2 3.0
VTRKL (V)
VTRKL (V)
2.9
2.9
VTRKL (V)
2.8 - 50 - 25
0
50 75 25 TEMPERATURE (C)
6
UW
100
4002 G13 4002 G16
TA = 25C, VCC = 10V unless otherwise noted. Current Mode Sense Voltage vs VCC
102 VBAT = 8V LTC4002-8.4
Current Mode Sense Voltage vs VCC
VBAT = 4V LTC4002-4.2
100
98 125
5
10
15 VCC (V)
20
25
4002 G14
98
5
10
15 VCC (V)
20
25
4002 G15
COMP Pin Output Current vs Temperature
VCOMP = 0V 86
NTC Pin Output Current vs VCC
VNTC = 0V
100
85
25
96 - 50 - 25
84 0 50 75 25 TEMPERATURE (C) 100 125
5
10
15 VCC (V)
20
25
4002 G18
4002 G17
Trickle Charge Voltage vs VCC
LTC4002-4.2 5.2
Trickle Charge Voltage vs Temperature
LTC4002-8.4
5.0
2.8 100 125
5
10
15 VCC (V)
20
25
4002 G20
4.8 - 50 - 25
0
50 75 25 TEMPERATURE (C)
100
125
4002 G19
4002 G21
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LTC4002 TYPICAL PERFOR A CE CHARACTERISTICS
Trickle Charge Voltage vs VCC
5.2 LTC4002-8.4 VBAT = 4V 10.4
VSNS (mV)
5.0
VSNS (mV)
VTRKL (V)
4.8
5
10
15 VCC (V)
20
Trickle Charge Sense Voltage vs Temperature
10.4 VBAT = 4V LTC4002-8.4
11
VSNS (mV)
VSNS (mV)
10.0
10
INTC (A)
9.6 - 50 - 25
0
50 75 25 TEMPERATURE (C)
End-of-Charge Ratio vs Temperature
29 LTC4002-4.2
28
REOC (%)
REOC (%)
25
21 - 50 - 25
UW
4002 G22
TA = 25C, VCC = 10V unless otherwise noted. Trickle Charge Sense Voltage vs VCC
11 VBAT = 2.5V LTC4002-4.2
Trickle Charge Sense Voltage vs Temperature
VBAT = 2.5V LTC4002-4.2
10.0
10
25
9.6 - 50 - 25
0
50 75 25 TEMPERATURE (C)
100
125
9
5
10
15 VCC (V)
20
25
4002 G24
4002 G23
Trickle Charge Sense Voltage vs VCC
VBAT = 4V LTC4002-8.4
NTC Pin Output Current vs Temperature
89 VNTC = 0V
85
100
125
9
5
10
15 VCC (V)
20
25
4002 G26
81 - 50 - 25
0
50 75 25 TEMPERATURE (C)
100
125
4002 G25
4002 G27
End-of-Charge Ratio vs VCC
LTC4002-4.2
25
22
0
50 75 25 TEMPERATURE (C)
100
125
5
10
15 VCC (V)
20
25
4002 G29
4002 G28
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7
LTC4002 TYPICAL PERFOR A CE CHARACTERISTICS
End-of-Charge Ratio vs Temperature
14 13 12 LTC4002-8.4
REOC (%)
REOC (%)
11 10 9 8 7 6 - 50 - 25 0 50 75 25 TEMPERATURE (C) 100 125
PI FU CTIO S
(DFN/SO-8)
COMP (Pin 1/Pin 1): Compensation, Soft-Start and Shutdown Control Pin. The COMP pin is the control signal of the inner loop of the current mode PWM. Charging begins when the COMP pin reaches 800mV. The recommended compensation components are a 0.47F (or larger) capacitor and a 2.2k series resistor. A 100A current into the compensation capacitor also sets the soft-start slew rate. Pulling the COMP pin below 360mV will shut down the charger. VCC (Pin 2/Pin 2): Positive Supply Voltage Input. VCC can range from VBAT(FLT) + 0.5V to 22V. A 0.1F or higher capacitor is required at the VCC pin with the lead length kept to a minimum. A 10F low ESR capacitor is also required at the source pins of the power P-channel MOSFET. GATE (Pin 3/Pin 3): Gate Drive Output. Driver Output for the P-Channel MOSFET. The voltage at this pin is internally clamped to 8V below VCC, allowing a low voltage MOSFET with gate-to-source breakdown voltage of 8V or less to be used. PGND, SGND, Exposed Pad, GND (Pins 4, 5, 11/Pin 4): IC Ground. The exposed pad (DFN) must be soldered to PCB ground to provide both electrical contact and optimum thermal performance. CHRG (Pin 6/Pin 5): Open-Drain Charge Status Output. When the battery is being charged, the CHRG pin is pulled low by an internal N-channel MOSFET. When the charge
8
UW
TA = 25C, VCC = 10V unless otherwise noted. End-of-Charge Ratio vs VCC
14 13 12 11 10 9 8 7 6
LTC4002-8.4
5
10
15 VCC (V)
20
25
4002 G31
4002 G30
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current drops below the End-of-Charge threshold for more than 120s, the N-channel MOSFET turns off and a 25A current source is connected from the CHRG pin to GND. When the timer runs out or the input supply is removed, the 25A current source is turned off and the CHRG pin becomes high impedance. BAT (Pin 7/Pin 6): Battery Sense Input. A bypass capacitor of 22F is required to minimize ripple voltage. An internal resistor divider, which is disconnected in sleep mode, sets the final float voltage at this pin. If the battery connection is opened when charging, an overvoltage circuit will limit the charger output voltage to 10% above the programmed float voltage. When VBAT is within 250mV of VCC, the LTC4002 is forced into sleep mode, dropping ICC to 10A. SENSE (Pin 8/Pin 7): Current Amplifier Sense Input. A sense resistor, RSENSE, must be connected between the SENSE and BAT pins. The maximum charge current is equal to 100mV/RSENSE. NTC (Pin 9/Pin 8): NTC (Negative Temperature Coefficient) Thermistor Input. With an external 10k NTC thermistor to ground, this pin senses the temperature of the battery pack and stops the charger when the temperature is out of range. When the voltage at this pin drops below 355mV at
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LTC4002
PI FU CTIO S
hot temperature or rises above 2.465V at cold temperature, charging is suspended and the internal timer stops. The CHRG pin output is not affected during this hold state. To
BLOCK DIAGRA
COMP
RSLOP
RIL 100mV SENSE
M1
M2
M3 90A
+
CSD 360mV CHRG SD
-
Q4 Q5 25A C/10 STOP
GND
+
-
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(DFN/SO-8)
disable the temperature qualification function, ground the NTC pin. NC (Pin 10/NA): No Connect.
VCC CLK: 100A ISLOP IL S Q CPWM R R CEOC 25mV or 10mV DRIVER
GATE
+ - +
CA
+-
-+
-
BAT
+
VA
- +
CLB
4.2V/CELL
- +
COV UVLO 4.2V
2.9V OR 5V
- +
CRQ
4.62V/CELL
UV
EOC RQ
LOGIC
- +
TEMP CCOLD
4.05V/CELL
2.465V VCC
NTC_DISABLE
- -
CHOT
85A
NTC
+ + -
355mV
4002 BD
50mV
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LTC4002
TEST CIRCUITS
Test Circuit 1
15V 1.5V
1.5V
Test Circuit 2
15V
LT1006
0V SENSE COMP 100A CA
BAT
RSENSE 10 1mA
COMP
100A CA
VA
4.2V
4002 TC02
LTC4002
OPERATIO
The LTC4002 is a constant current, constant voltage Li-Ion battery charger controller that uses a current mode PWM step-down (buck) switching architecture. The charge current is set by an external sense resistor (RSENSE) across the SENSE and BAT pins. The final battery float voltage is internally set to 4.2V per cell. For batteries like lithium-ion that require accurate final float voltage, the internal 2.465V reference, voltage amplifier and the resistor divider provide regulation with 1% accuracy. A charge cycle begins when the voltage at the VCC pin rises above the UVLO level and is 250mV or more greater than the battery voltage. At the beginning of the charge cycle, if the battery voltage is less than the trickle charge threshold, 2.9V for the 4.2 version and 5V for the 8.4 version, the charger goes into trickle charge mode. The trickle charge current is internally set to 10% of the full-scale current. If the battery voltage stays low for 30 minutes, the battery is considered faulty and the charge cycle is terminated. When the battery voltage exceeds the trickle charge threshold, the charger goes into the full-scale constant current
charge mode. In constant current mode, the charge current is set by the external sense resistor RSENSE and an internal 100mV reference; IBAT = 100mV/RSENSE. When the battery voltage approaches the programmed float voltage, the charge current will start to decrease. When the current drops to 25% (4.2 version) or 10% (8.4 version) of the full-scale charge current, an internal comparator turns off the internal pull-down N-channel MOSFET at the CHRG pin, and connects a weak current source to ground to indicate a near end-of-charge condition. An internal 3 hour timer determines the total charge time. After a time out occurs, the charge cycle is terminated and the CHRG pin is forced high impedance. To restart the charge cycle, remove and reapply the input voltage or momentarily shut the charger down. Also, a new charge cycle will begin if the battery voltage drops below the recharge threshold voltage of 4.05V per cell. When the input voltage is present, the charger can be shut down (ICC = 3mA) by pulling the COMP pin low. When the input voltage is not present, the charger goes into sleep
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10
-
+
+
0V LTC4002 SENSE RSENSE 10 VBAT
4002 TC01
-
LT1006 BAT
-
-
+
+
U
+
-
LTC4002
OPERATIO
mode, dropping ICC to 10A. This will greatly reduce the current drain on the battery and increase the standby time. A 10k NTC (negative temperature coefficient) thermistor can be connected from the NTC pin to ground for battery
APPLICATIO S I FOR ATIO
Undervoltage Lockout (UVLO)
An undervoltage lockout circuit monitors the input voltage and keeps the charger off until VCC rises above the UVLO threshold (4.2V for the 4.2 version, 7.5V for the 8.4 version) and at least 250mV above the battery voltage. To prevent oscillation around the threshold voltage, the UVLO circuit has 200mV per cell of built-in hysteresis. When specifying minimum input voltage requirements, the voltage drop across the input blocking diode must be added to the minimum VCC supply voltage specification. Trickle Charge and Defective Battery Detection At the beginning of a charge cycle, if the battery voltage is below the trickle charge threshold, the charger goes into trickle charge mode with the charge current reduced to 10% of the full-scale current. If the low-battery voltage persists for 30 minutes, the battery is considered defective, the charge cycle is terminated and the CHRG pin is forced high impedance. Shutdown The LTC4002 can be shut down by pulling the COMP pin to ground which pulls the GATE pin high turning off the external P-channel MOSFET. When the COMP pin is released, the internal timer is reset and a new charge cycle starts. In shutdown, the output of the CHRG pin is high impedance and the quiescent current remains at 3mA. Removing the input power supply will put the charger into sleep mode. If the voltage at the VCC pin drops below (VBAT + 250mV) or below the UVLO level, the LTC4002 goes into a low current (ICC = 10A) sleep mode, reducing the battery drain current.
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UU
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temperature qualification. The charge cycle is suspended when the temperature is outside of the 0C to 50C window (with DALE NTHS-1206N02). CHRG Status Output Pin When a charge cycle starts, the CHRG pin is pulled to ground by an internal N-channel MOSFET which is capable of driving an LED. When the charge current drops below the End-of-Charge threshold for more than 120s, the N-channel MOSFET turns off and a weak 25A current source to ground is connected to the CHRG pin. This weak 25A pull-down remains until the timer ends the charge cycle, or the charger is in manual shutdown or sleep mode. After a time out occurs (charge cycle ends), the pin will become high impedance. By using two different value resistors, a microprocessor can detect three states from this pin (charging, end-of-charge and charging stopped) see Figure 1.
VCC VDD LTC4002 CHRG 390k 2k PROCESSOR OUT IN
4002 F02
Figure 1. Microprocessor Interface
To detect the charge mode, force the digital output pin, OUT, high and measure the voltage at the CHRG pin. The N-channel MOSFET will pull the pin low even with a 2k pull-up resistor. Once the charge current drops below the End-of-Charge threshold, the N-channel MOSFET is turned off and a 25A current source is connected to the CHRG pin. The IN pin will then be pulled high by the 2k resistor connected to OUT. Now force the OUT pin into a high
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11
LTC4002
APPLICATIO S I FOR ATIO
impedance state, the current source will pull the pin low through the 390k resistor. When the internal timer has expired, the CHRG pin changes to a high impedance state and the 390k resistor will then pull the pin high to indicate charging has stopped. Gate Drive The LTC4002 gate driver can provide high transient currents to drive the external pass transistor. The rise and fall times are typically 20ns and 50ns respectively when driving a 2000pF load, which is typical for a P-channel MOSFET with RDS(ON) in the range of 50m. A voltage clamp is added to limit the gate drive to 8V below VCC. For example, if VCC is 10V then the GATE output will pull down to 2V max. This allows low voltage P-channel MOSFETs with superior RDS(ON) to be used as the pass transistor thus increasing efficiency. Stability Both the current loop and the voltage loop share a common, high impedance, compensation node (COMP pin). A series capacitor and resistor on this pin compensates both loops. The resistor is included to provide a zero in the loop response and boost the phase margin. The compensation capacitor also provides a soft-start function for the charger. Upon start-up, the COMP pin voltage will quickly rise to 0.22V, due to the 2.2k series resistor, then ramp at a rate set by the internal 100A pullup current source and the external capacitor. Battery charge current starts ramping up when the COMP pin voltage reaches 0.8V and full current is achieved with the
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COMP pin at 1.3V. With a 0.47F capacitor, time to reach full charge current is about 2.35ms. Capacitance can be increased up to 1F if a longer start-up time is needed. Automatic Battery Recharge After the 3 hour charge cycle is completed and both the battery and the input power supply (wall adapter) are still connected, a new charge cycle will begin if the battery voltage drops below 4.05V per cell due to self-discharge or external loading. This will keep the battery capacity at more than 80% at all times without manually restarting the charge cycle. Battery Temperature Detection A negative temperature coefficient (NTC) thermistor located close to the battery pack can be used to monitor battery temperature and will not allow charging unless the battery temperature is within an acceptable range. Connect a 10k thermistor (DALE NTHS-1206N02) from the NTC pin to ground. If the temperature rises to 50C, the resistance of the NTC will be approximately 4.1k. With the 85A pull-up current source, the Hot temperature voltage threshold is 350mV. For Cold temperature, the voltage threshold is set at 2.465V which is equal to 0C (RNTC 28.4k) with 85A of pull-up current. If the temperature is outside the window, the GATE pin will be pulled up to VCC and the timer frozen while the output status at the CHRG pin remains the same. The charge cycle begins or resumes once the temperature is within the acceptable range. Short the NTC pin to ground to disable the temperature qualification feature.
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LTC4002
APPLICATIO S I FOR ATIO
Input and Output Capacitors Since the input capacitor is assumed to absorb all input switching ripple current in the converter, it must have an adequate ripple current rating. Worst-case RMS ripple current is approximately one-half of output charge current. Actual capacitance value is not critical. Solid tantalum capacitors have a high ripple current rating in a relatively small surface mount package, but caution must be used when tantalum capacitors are used for input bypass. High input surge currents can be created when the adapter is hot-plugged to the charger and solid tantalum capacitors have a known failure mechanism when subjected to very high turn-on surge currents. Selecting the highest possible voltage rating on the capacitor will minimize problems. Consult with the manufacturer before use. The selection of output capacitor COUT is primarily determined by the ESR required to minimize ripple voltage and load step transients. The output ripple VOUT is approximately bounded by:
1 VOUT IL ESR + 8 fOSCCOUT
Since IL increases with input voltage, the output ripple is highest at maximum input voltage. Typically, once the ESR requirement is satisfied, the capacitance is adequate for filtering and has the necessary RMS current rating.
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Switching ripple current splits between the battery and the output capacitor depending on the ESR of the output capacitor and the battery impedance. EMI considerations usually make it desirable to minimize ripple current in the battery leads. Ferrite beads or an inductor may be added to increase battery impedance at the 500kHz switching frequency. If the ESR of the output capacitor is 0.2 and the battery impedance is raised to 4 with a bead or inductor, only 5% of the current ripple will flow in the battery. Design Example As a design example, take a charger with the following specifications: VIN = 5V to 22V, VBAT = 4V nominal, IBAT = 1.5A, fOSC = 500kHz, see Figure 2. First, calculate the SENSE resistor : RSENSE = 100mV/1.5A = 68m Choose the inductor for about 65% ripple current at the maximum VIN:
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L=
4V 4V 1- = 6.713H (500kHz)(0.65)(1.5A) 22V
Selecting a standard value of 6.8H results in a maximum ripple current of :
IL =
4V 4V 1- = 962.6mA (500kHz)(6.8H) 22V
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LTC4002
APPLICATIO S I FOR ATIO
Next, choose the P-channel MOSFET. The Si6435ADQ in a TSSOP-8 package with RDS(ON) = 42m (nom), 55m (max) offers a small solution. The maximum power dissipation with VIN = 5V and VBAT = 4V at 50C ambient temperature is:
(1.5A) (55m )(4V) = 0.099 W PD = 5V TJ = 50C + (0.099W)(65C/W) = 56.5C
CIN is chosen for an RMS current rating of about 0.8A at 85C. The output capacitor is chosen for an ESR similar to the battery impedance of about 100m. The ripple voltage on the BAT pin is:
IL(MAX) (ESR) 2 (0.96A)(0.1) = 48mV = 2 C1: Taiyo Yuden TMK325BJ106MM C2: Taiyo Yuden JMK325BJ226MM L1: TOKO B952AS-6R8N VOUT(RIPPLE) =
2
The Schottky diode D2 shown in Figure 2 conducts current when the pass transistor is off. In a low duty cycle case, the current rating should be the same or higher than the charge current. Also it should withstand reverse voltage as high as VIN.
BAT R1 2k CHARGE STATUS
RC 2.2k
Figure 2. 1.5A Single Cell Li-Ion Battery Charger
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Board Layout Suggestions When laying out the printed circuit board, the following considerations should be taken to ensure proper operation of the LTC4002. GATE pin rise and fall times are 20ns and 50ns respectively (with CGATE = 2000pF). To minimize radiation, the catch diode, pass transistor and the input bypass capacitor traces should be kept as short as possible. The positive side of the input capacitor should be close to the source of the P-channel MOSFET; it provides the AC current to the pass transistor. The connection between the catch diode and the pass transistor should also be kept as short as possible. The SENSE and BAT pins should be connected directly to the sense resistor (Kelvin sensing) for best charge current accuracy. Avoid routing the NTC PC board trace near the MOSFET switch to minimize coupling switching noise into the NTC pin. The compensation capacitor connected at the COMP pin should return to the ground pin of the IC or as close to it as possible. This will prevent ground noise from disrupting the loop stability. The ground pin also works as a heat sink, therefore use a generous amount of copper around the ground pin. This is especially important for high VCC and/or high gate capacitance applications.
VIN 5V TO 22V D1 B330 C3 0.1F CER 2 VCC GATE LTC4002ES8-4.2 5 7 L1 6.8H RSENSE 68m 3 M1 Si6435ADQ C1 10F CER D2 B330 CHRG SENSE 1 CC 0.47F COMP NTC 8 T 10k NTC BAT GND 4 6 C2 22F CER
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4.2V Li-Ion BATTERY
4002 F02
NTC: DALE NTHS-1206N02
LTC4002
PACKAGE DESCRIPTIO
3.50 0.05 1.65 0.05 2.15 0.05 (2 SIDES) PACKAGE OUTLINE 0.25 0.05 0.50 BSC 2.38 0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS PIN 1 TOP MARK (SEE NOTE 6)
.050 BSC
8
.245 MIN
.030 .005 TYP
RECOMMENDED SOLDER PAD LAYOUT .010 - .020 x 45 (0.254 - 0.508) .008 - .010 (0.203 - 0.254) 0- 8 TYP
.016 - .050 (0.406 - 1.270)
NOTE: 1. DIMENSIONS IN
INCHES (MILLIMETERS) 2. DRAWING NOT TO SCALE 3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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DD Package 10-Lead Plastic DFN (3mm x 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115 TYP 6 0.675 0.05 0.38 0.10 10 3.00 0.10 (4 SIDES) 1.65 0.10 (2 SIDES)
(DD10) DFN 1103
5 0.200 REF 0.75 0.05 2.38 0.10 (2 SIDES)
1 0.25 0.05 0.50 BSC
0.00 - 0.05
BOTTOM VIEW--EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE
S8 Package 8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.189 - .197 (4.801 - 5.004) NOTE 3 7 6 5
.045 .005
.160 .005 .228 - .244 (5.791 - 6.197)
.150 - .157 (3.810 - 3.988) NOTE 3
1
2
3
4
.053 - .069 (1.346 - 1.752)
.004 - .010 (0.101 - 0.254)
.014 - .019 (0.355 - 0.483) TYP
.050 (1.270) BSC
SO8 0303
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LTC4002
TYPICAL APPLICATIO
RELATED PARTS
PART NUMBER LTC1732-8.4 LTC1733 DESCRIPTION 2-Cell Li-Ion Linear Battery Charger Li-Ion Battery Charger with Termal Regulation COMMENTS 8.8V VIN 12V; Programmable Charge Termination Timer Standalone Charger Standalone Charger, Constant-Current/Constant-Voltage/ Constant-Temperature, Integrated MOSFET, No External Sense Resistor or Blocking Diodes Need Only Two External Components, Monitors Charge Current, No Reverse Diode or Sense Resistor Required, 50mA to 700mA Wall Adapter May Be Above or Below Battery Voltage, Standalone, 1-, 2-Cell Li-Ion, Also for Charging NiMH and NiCd Batteries 6V VIN 28V, High Efficiency 90%, VOUT 28V, Digital Interface I/O, Small Inductor 0.35 Internal N-FET Requires No Blocking Diode, Current Limit for Safety Charges from USB Input or AC/DC, 100mA/500mA Up to 1.25A, Thermal Regulation, Fully Integrated Thermal Regulation Prevents Overheating, C/10 Termination, C/10 Indicator Charge Termination Included, ICH 700mA, 8-Lead ThinSOT Package Automatic Switching Between DC Sources, Simplified Load Sharing
LTC1734/LTC1734L LTC1980 LTC4006/LTC4007 LTC4008 LTC4052/LTC1730 LTC4053 LTC4054 LTC4056 LTC4412/LTC4413
SOT-23 Li-Ion Battery Chargers Combination Battery Charger and DC/DC Converter 4A Multiple Cell Li-Ion, NiCd, NiMH, Lead Acid Battery Chargers Integrated Pulse Chargers for a 1-Cell Li-Ion Battery USB Compatible Li-Ion Linear Battery Charger Standalone Linear Li-Ion Battery Charger with Integrated Pass Transistor in ThinSOTTM Standalone SOT-23 Li-Ion Linear Battery Charger Low Loss PowerPath Controllers in ThinSOT
TM
PowerPath and ThinSOT are trademarks of Linear Technology Corporation.
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507
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2-Cell 8.4V, 2A Li-Ion Battery Charger
R1 100k VIN 9V TO 12V M2 1/2 Si9933ADY C3 0.1F CER 2 VCC GATE 3 M1 1/2 Si9933ADY D2 B330 C1 10F CER LTC4002ES8-8.4 5 7 RSENSE 50m C2 22F CER L1 6.8H CHRG SENSE 1 CC 0.47F RC 2.2k COMP NTC 8 T 10k NTC BAT GND 4 6
+
8.4V Li-Ion BATTERY
4002 TA03
NTC: DALE NTHS-1206N02
4002f LT/TP 1104 1K PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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